System.Threading.CountdownEvent 是一个同步基元，它在收到一定次数的信号之后，将会解除对其等待线程的锁定。 CountdownEvent 专门用于以下情况：您必须使用 ManualResetEvent 或 ManualResetEventSlim，并且必须在用信号通知事件之前手动递减一个变量。 例如，在分叉/联接方案中，您可以只创建一个信号计数为 5 的 CountdownEvent，然后在线程池上启动五个工作项，并且让每个工作项在完成时调用 Signal。每次调用 Signal 时，信号计数都会递减 1。 在主线程上，对 Wait 的调用将会阻塞，直至信号计数为零。
CountdownEvent 具有这些附加功能：
•可通过使用取消标记来取消等待操作。
•创建实例之后可以递增它的信号计数。
•通过调用 Reset 方法，可在 Wait 返回之后重用实例。
•实例公开 WaitHandle 以便与其他 .NET Framework 同步 API（例如 WaitAll）进行集成。——MSDN
1.普通示例
usingSystem;usingSystem.Threading;usingSystem.Threading.Tasks;namespaceConsoleapplication18
{classPRogram
{staticCountdownEvent cde =null;/// <summary>/// 模拟建房子/// </summary>/// <param name="args"></param>staticvoidMain(string[] args)
{//建房子第一期工人string[] _bhPerson1 =newstring[5] {"Yan","Zhi","wei","Do","Work"};//建房子第二期工人string[] _bhPerson2 =newstring[3] {"Yan2","Zhi2","wei2"};//建房子第三期工人string[] _bhPerson3 =newstring[3] {"Yan3","Zhi3","wei3"};using(cde =newCountdownEvent(Environment.ProcessorCount))//开始监管，相当于监工{cde.Reset(_bhPerson1.Length);//设置第一期建造需要5个人foreach(stringpersonin_bhPerson1)
{
Task.Factory.StartNew(() =>
{
BuilderHourseStep1(person);
});
}cde.Wait();//等待第一期建造完成Console.WriteLine("-----------------------");
cde.Reset(_bhPerson2.Length);//设置第二期建需要三个人foreach(stringpersonin_bhPerson2)
{
Task.Factory.StartNew(() =>
{
BuilderHourseStep2(person);
});
}
cde.Wait();//等待第二期建造完成Console.WriteLine("-----------------------");
cde.Reset(_bhPerson3.Length);//设置第三期建需要三个人foreach(stringpersonin_bhPerson3)
{
Task.Factory.StartNew(() =>
{
BuilderHourseStep3(person);
});
}
cde.Wait();//等待第三期建造完成Console.WriteLine("-----------------------");
}
}/// <summary>/// 建房子第一道所需要的工序/// </summary>/// <param name="person"></param>staticvoidBuilderHourseStep1(stringperson)
{try{
Console.WriteLine(string.Format("『{0}』BuilderHourseStep1....", person));
}finally{cde.Signal();//建造完成一点后，通知监工}
}/// <summary>/// 建房子第二道所需要的工序/// </summary>/// <param name="person"></param>staticvoidBuilderHourseStep2(stringperson)
{try{
Console.WriteLine(string.Format("『{0}』BuilderHourseStep2.....", person));
}finally{
cde.Signal();
}
}/// <summary>/// 建房子第三道所需要的工序/// </summary>/// <param name="person"></param>staticvoidBuilderHourseStep3(stringperson)
{try{
Console.WriteLine(string.Format("『{0}』BuilderHourseStep3.......", person));
}finally{
cde.Signal();
}
}
}
}
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2.超时演示，延续上面例子，建造房子存在延期的情况，譬如某个工作工作懒散，那么需要给整个一期建造设置一个总的时限。
usingSystem;usingSystem.Threading;usingSystem.Threading.Tasks;namespaceConsoleApplication18
{classProgram
{staticCountdownEvent cde =null;staticintoverLimitTime = 5000;//第一期工作完成时间/// <summary>/// 模拟建房子/// </summary>/// <param name="args"></param>staticvoidMain(string[] args)
{try{//建房子第一期工人string[] _bhPerson1 =newstring[5] {"Yan","Zhi","wei","Do","Work"};//建房子第二期工人string[] _bhPerson2 =newstring[3] {"Yan2","Zhi2","wei2"};//建房子第三期工人string[] _bhPerson3 =newstring[3] {"Yan3","Zhi3","wei3"};using(cde =newCountdownEvent(Environment.ProcessorCount))//开始监管，相当于监工{
cde.Reset(_bhPerson1.Length);//设置第一期建造需要5个人Random _workTime =newRandom();foreach(stringpersonin_bhPerson1)
{
Task.Factory.StartNew(() =>
{int_doWorkTime = _workTime.Next(3000, 6000);//工人工作时间BuilderHourseStep1(person, _doWorkTime);
});
}bool_bdStep1Result = cde.Wait(overLimitTime);
Console.WriteLine(string.Format("第一期建造状态：{0}.", _bdStep1Result ==true?"完成":"延时"));//等待第一期建造完成 限制5秒内完成Console.WriteLine("-----------------------");if(!_bdStep1Result)return;
cde.Reset(_bhPerson2.Length);//设置第二期建需要三个人foreach(stringpersonin_bhPerson2)
{
Task.Factory.StartNew(() =>
{
BuilderHourseStep2(person);
});
}
cde.Wait();//等待第二期建造完成Console.WriteLine("-----------------------");
cde.Reset(_bhPerson3.Length);//设置第三期建需要三个人foreach(stringpersonin_bhPerson3)
{
Task.Factory.StartNew(() =>
{
BuilderHourseStep3(person);
});
}
cde.Wait();//等待第三期建造完成Console.WriteLine("-----------------------");
}
}catch(Exception ex)
{
Console.WriteLine(string.Format("Excepton Message: {0}", ex.Message.Trim()));
}finally{
Console.ReadLine();
}
}/// <summary>/// 建房子第一道所需要的工序/// </summary>/// <param name="person"></param>staticvoidBuilderHourseStep1(stringperson,intdoWorkTime)
{bool_isDoWork = doWorkTime < overLimitTime;try{if(_isDoWork)
Console.WriteLine(string.Format("『{0}』做事情花费了,{1}s........", person, doWorkTime));elseConsole.WriteLine(string.Format("『{0}』做事情太墨迹，花费了{1}s....", person, doWorkTime));
Thread.Sleep(doWorkTime);
}finally{if(_isDoWork)
cde.Signal();//建造完成后，通知监工}}/// <summary>/// 建房子第二道所需要的工序/// </summary>/// <param name="person"></param>staticvoidBuilderHourseStep2(stringperson)
{try{
Console.WriteLine(string.Format("『{0}』BuilderHourseStep2.....", person));
}finally{
cde.Signal();
}
}/// <summary>/// 建房子第三道所需要的工序/// </summary>/// <param name="person"></param>staticvoidBuilderHourseStep3(stringperson)
{try{
Console.WriteLine(string.Format("『{0}』BuilderHourseStep3.......", person));
}finally{
cde.Signal();
}
}
}
}
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